The planning, testing, implementing, and auditing of patches.
Planning- Decide if patch is necessary/compatible with other systems. Microsoft Basline Security Analyzer (MBSA) is a good program to use on the network to find security weaknesses.
Testing- Testing of the patch/hotfix on a "test" machine or machines, is a great way of making sure that no problems occur after they are implemented.
Implementing- If test is good, deploy the patch. This is done in the evening or over the weekend. Software such as Microsofts Systerms Management Server (SMS) or Windows Server Udate Services (WSUS).
Auditing- After implemation, check to see if the patch/hotfix has taken hold, then check for any changes of failures due the patch/hotfix.